Urticating hairs information wanted

[Rich.Harrington]

One for the more academically minded here, We all know what urticating hairs are and that they are found on new world species. I was wondering though, are they a new development among theraphosids or not?

Are the new world species further along the evolutionary chain or such?

[Ian Shaw]

I am not one of the academics you were looking for Rich but this thought has crossed my mind as well. I thought the old world tarantulas had more powerful chelicera instead of urticating hairs. So they have gone off on a evolutionary tangent in a sense. I am not sure but hopefully some one has a better idea.

[James Box]

i've no idea how advanced or non-advanced T's are, but i have heard strange tales of Old World T's kicking imaginary urticating hairs at their owners. strange behaviour even as a possible vestigial instinct...
i've no idea what it means!

[Clinton Hogben]

We all know what urticating hairs are and that they are found on new world species. I was wondering though, are they a new development among theraphosids or not?

Are the new world species further along the evolutionary chain or such?

Hi Rich
Stan may know the answer he had a thread about urticating hairs a while back as he was doing some research for another book you could try him

Clint

http://thebts.co.uk/forums/showthread.php?t=3249

[jason holland]

ive read somewhere that the reasons why new world have them, but old don't is due to how aggresive they are. eg

the old world (eg the baboons etc) tend to be more agressive and so use that to defend / warn off prey

whereas the new world addopted the "if you come near me ill shoot you" defense,

so i dont think you could say that the new world T's are more evolved, id just say its down to the spiders personality's and behavours etc... dunno if that just confuses things lol

[Chris Hamilton]

Urticating hairs are an evolutionary adaptation to the New World. It doesn't mean that they are "more advanced" than the Old World...bad phrasing b/c they have been evolving for the same amount of time...
And some New World T's don't have them...was the common ancestor(s) that started the New World T's a spider that possessed UT's? or didn't and then that character evolved? We don't know...it's not clear yet. The most parsimonious path is that they didn't have them at first and then evolved that trait and it spread rapidly through the New World because of how advantageous it was. UT's are highly effective against small mammals...the main predators of tarantulas (by blinding or getting into the nasal or throat passages and causing them to inflame and cutoff air.
The Old World T's do not have them...they have evolved other behaviors to deal with possible predators.

[Phil Rea]

The most parsimonious path is that they didn't have them at first and then evolved that trait and it spread rapidly through the New World because of how advantageous it was.

Parsimony? We have a cladist amongst us

I don't know enough about spider evolution to directly comment on which evolved first, but spiders have been around since the Devonian, (and the old world and the new world have been separate since the Jurassic if I remember correctly), so isolated populations have had plenty of time to take different evolutionary paths.

As Chris says, neither are more advanced in an evolutionary sense (as they are all of the Family theraphosidae), but they are simply separate advantageous adaptations to their environment and are a divergent modification from the common ancestor of both (however far back in the 'tree' that may be).